[gcc r15-354] [committed] [RISC-V] Provide splitting guidance to combine to faciliate shNadd.uw generation

[gcc r15-354] [committed] [RISC-V] Provide splitting guidance to combine to faciliate shNadd.uw generation

[Jeff Law]

https://gcc.gnu.org/g:bfb88b1406cdd8d3f97e280b0d63529aa925f18a

commit r15-354-gbfb88b1406cdd8d3f97e280b0d63529aa925f18a
Author: Jeff Law <jlaw@ventanamicro.com>
Date:   Thu May 9 21:07:06 2024 -0600

    [committed] [RISC-V] Provide splitting guidance to combine to faciliate shNadd.uw generation
    
    This fixes a minor code quality issue I found while comparing GCC and LLVM.
    Essentially we want to do a bit of re-association to generate shNadd.uw
    instructions.
    
    Combine does the right thing and finds all the necessary instructions,
    reassociates the operands, combines constants, etc.  Where is fails is finding
    a good split point.  The backend can trivially provide guidance on how to split
    via a define_split pattern.
    
    This has survived both Ventana's internal CI system (rv64gcb) as well as my own
    (rv64gc, rv32gcv).
    
    I'll wait for the external CI system to give the all-clear before pushing.
    
    gcc/
            * config/riscv/bitmanip.md: Add splitter for shadd feeding another
            add instruction.
    
    gcc/testsuite/
    
            * gcc.target/riscv/zba-shadduw.c: New test.

Diff:
---
 gcc/config/riscv/bitmanip.md                 | 17 ++++++++++++++
 gcc/testsuite/gcc.target/riscv/zba-shadduw.c | 35 ++++++++++++++++++++++++++++
 2 files changed, 52 insertions(+)

diff --git a/gcc/config/riscv/bitmanip.md b/gcc/config/riscv/bitmanip.md
index ad3ad758959e..d76a72d30e02 100644
--- a/gcc/config/riscv/bitmanip.md
+++ b/gcc/config/riscv/bitmanip.md
@@ -184,6 +184,23 @@
   [(set_attr "type" "bitmanip")
    (set_attr "mode" "DI")])
 
+;; Combine will reassociate the operands in the most useful way here.  We
+;; just have to give it guidance on where to split the result to facilitate
+;; shNadd.uw generation.
+(define_split
+  [(set (match_operand:DI 0 "register_operand")
+	(plus:DI (plus:DI (and:DI (ashift:DI (match_operand:DI 1 "register_operand")
+					     (match_operand:QI 2 "imm123_operand"))
+				  (match_operand 3 "consecutive_bits32_operand"))
+			  (match_operand:DI 4 "register_operand"))
+		 (match_operand 5 "immediate_operand")))]
+  "TARGET_64BIT && TARGET_ZBA"
+  [(set (match_dup 0)
+	(plus:DI (and:DI (ashift:DI (match_dup 1) (match_dup 2))
+			 (match_dup 3))
+		 (match_dup 4)))
+   (set (match_dup 0) (plus:DI (match_dup 0) (match_dup 5)))])
+
 ;; ZBB extension.
 
 (define_expand "clzdi2"
diff --git a/gcc/testsuite/gcc.target/riscv/zba-shadduw.c b/gcc/testsuite/gcc.target/riscv/zba-shadduw.c
new file mode 100644
index 000000000000..5b77447e6813
--- /dev/null
+++ b/gcc/testsuite/gcc.target/riscv/zba-shadduw.c
@@ -0,0 +1,35 @@
+/* { dg-do compile } */
+/* { dg-options "-O2 -march=rv64gc_zba -mabi=lp64" } */
+
+typedef struct simple_bitmap_def
+{
+  unsigned char *popcount;
+  unsigned int n_bits;
+  unsigned int size;
+  unsigned long elms[1];
+} *sbitmap;
+typedef const struct simple_bitmap_def *const_sbitmap;
+
+typedef unsigned long *sbitmap_ptr;
+typedef const unsigned long *const_sbitmap_ptr;
+static unsigned long sbitmap_elt_popcount (unsigned long);
+
+void
+sbitmap_a_or_b (sbitmap dst, const_sbitmap a, const_sbitmap b)
+{
+  unsigned int i, n = dst->size;
+  sbitmap_ptr dstp = dst->elms;
+  const_sbitmap_ptr ap = a->elms;
+  const_sbitmap_ptr bp = b->elms;
+  unsigned char has_popcount = dst->popcount != ((void *) 0);
+
+  for (i = 0; i < n; i++)
+    {
+      const unsigned long tmp = *ap++ | *bp++;
+      *dstp++ = tmp;
+    }
+}
+
+
+/* { dg-final { scan-assembler "sh3add.uw" } } */
+/* { dg-final { scan-assembler-not {\mslli.uw} } } */